The Reliability Files
EP Editorial Staff | September 18, 2013
Fouled Heat Exchangers?
Try Electronic Water Treatment
When material deposits form on heat-transfer surfaces, fouling occurs. Common fouling mechanisms include particulates, crystals (usually calcium carbonate), biological organisms, chemical reactions and corrosion. Fouling significantly impacts the thermal and mechanical performance of heat exchangers by increasing overall thermal resistance and lowering the overall heat-transfer coefficient. It also impedes fluid flow, accelerates corrosion and reduces pressure across the heat exchanger.
Fouling adds to energy costs because of the additional energy required to overcome its effects. Estimates place these fouling-related costs in the billions of dollars annually across industry. Additional costs are attributed to maintenance charges for the removal of fouling deposits. According to heat-exchanger manufacturers, 15% of all factory maintenance costs are related to heat-exchanger problems, and half of these problems are due to fouling. Factor in downtime caused by fouling and the effect of the problem is only too plain.
Cleaning fouled heat exchangers is the solution, and can be accomplished in several ways: mechanically, with brushes and scrapers; chemically, with solvents; with high-velocity water pressure; and with electronic water treatment. Of these, electronic water treatment (EWT) may be the most effective, according to numerous studies conducted around the world. Not only does this form of cleaning work with rust (corrosion) and scale, it works on biological fouling such as zebra mussels.
To understand how electronic scale removal works, it is first important to understand the factors that cause scale. While scale can be a complex of many minerals, the most common in industrial processes is calcium carbonate. Calcium carbonate can form spontaneously when aqueous solutions become supersaturated, which means that they contain higher concentrations of dissolved substance than their equilibrium concentration. Such solutions are unstable, and easily triggered into dropping back to saturation level, forcing the dissolved compound to separate from the solution and form scales. Other factors that contribute to scale formation include pH levels and temperature, where high levels of either promote scale formation, and fluid pressure, where low levels promote scale formation.
Electronic water treatment (EWT) is a non-invasive system that uses a solenoid coil or coils wrapped around the pipework to be treated. A signal generator that creates a continuously changing frequency supplies current to the coils. The pulsing current creates an induced electric field around the axis inside the pipe. In this arrangement, any charged particle or ion moving within the field experiences a so-called Lorentz force, which is generated by the interaction between charged particles and magnetic and electric fields. This alters the number, size and shape of the crystals (making them smaller and more round) which, in turn, will reduce adherence and buildup on the pipe wall. The crystals will be carried away with the water flow. As no new scale layers are formed, existing scale layers will be gradually removed by the sheer force of the water flow.
Return On Investment
EWT is an effective, environmentally friendly, cost-efficient way of reducing heat-exchanger fouling and achieving the following benefits:
- Lower water and energy bills
- Extended piping and equipment life
- Increased mean time before equipment failure
- Installation without plant shutdown
- A 20-year-plus life span
Scalewatcher North America, Inc.